An engine control module of an internal combustion engine controls the mixture of fuel and air supplied to combustion chambers of the engine. After the air/fuel mixture is ignited, combustion takes place and later the combustion gases exit the combustion chambers through exhaust valves. The combustion gases are directed by an exhaust manifold to a catalytic converter or other exhaust aftertreatment systems.
Manufacturers of internal combustion engines, particularly diesel engines, are presented with the challenging task of complying with current and future emission standards for the release of nitrogen oxides, particularly nitrogen monoxide, as well as unburned and partially oxidized hydrocarbons, carbon monoxide, particulate matter, and other pollutants. In order to reduce the exhaust emissions of an internal combustion engine, an exhaust gas aftertreatment system is used to reduce regulated emissions within the exhaust gas flowing from the engine.
Exhaust gas aftertreatment systems typically include one or more aftertreatment devices, such as, particulate filters, catalytic converters, mixing elements and urea/fuel injectors. Variations in exhaust gas flow, such as lack of uniform flow, can adversely affect the performance of the aftertreatment system, thus causing unwanted exhaust constituents to be released from the system. As emissions standards become increasingly stringent, improving the uniformity and distribution of the exhaust gas flow as it enters and flows through the aftertreatment system is desirable in meeting those standards. Exhaust gas flow uniformity may be enhanced by lengthening the flow path of the exhaust gas, however, packaging restrictions in modern vehicles may prevent designs with long flow paths. Further, some aftertreatment devices perform more efficiently when heated to a certain temperature. Therefore, a long exhaust gas flow path can lead to inefficient exhaust treatment, due to the larger thermal mass and resulting thermal losses as the exhaust gas flows along the path. Accordingly, several factors affect the design of exhaust aftertreatment systems.
Exhaust emissions may also be reduced by utilizing exhaust gas recirculation (EGR) techniques. Efficient use of EGR generally supports the objectives of realizing high power output from engines while also achieving higher fuel efficiency and economy and achieving increasingly stringent engine emission requirements. However, as engines become more complex, the packaging of various components can make the design of EGR systems in combination with exhaust aftertreatment systems more challenging.
Accordingly, achieving desired emissions reductions while improving efficiency may be challenging in view of modern vehicle packaging requirements and limitations.